This invention relates to a trench-gate semiconductor device including a region comprising a narrow-bandgap semiconductor material. In particular, the invention provides a trench-gate power semiconductor device such as, for example, an insulated-gate field-effect transistor (commonly termed a power MOSFET).
United States patent specification U.S. Pat. No. 5,698,869 discloses a trench-gate semiconductor device comprising a semiconductor body having a first major surface from which a trench-gate structure extends into the body. The body includes a body region of a first conductivity type which extends adjacent to the trench-gate structure. This body region provides the device with a channel-accommodating portion between first and second regions of an opposite second conductivity type in a current-carrying path of the device. The first region comprises a narrow-bandgap semiconductor material which is of the second conductivity type and of narrower energy bandgap than the semiconductor body so providing a heterojunction. The whole contents of U.S. Pat. No. 5,698,869 are hereby incorporated herein as reference material.
The devices disclosed in U.S. Pat. No. 5,698,869 have their body region at a floating potential, which in most cases is due to a so-called SOI (silicon on insulator) formation for the device. The inclusion of the narrow-bandgap semiconductor material suppresses this "floating body effect", reducing leakage current across the device and improving drain breakdown voltage. Most embodiments in U.S. Pat. No. 5,698,869 are DRAM (dynamic random access memory) cells, the holding characteristics of which are improved by the inclusion of the narrow-bandgap semiconductor material in an interior of a drain region of the DRAM cell-select transistor. This drain region is formed adjacent to the trenched, first major surface of the semiconductor body. In these embodiments, the narrow-bandgap semiconductor material is formed in this region by ion implantation, and particularly by implantation of germanium ions into monocrystalline silicon.